Effects of various power system stabilizers on improving power system dynamic performance

To ensure the small-signal stability of a power system, power system stabilizers (PSSs) are extensively applied for damping low frequency power oscillations through modulating the excitation supplied to synchronous machines, and increasing interest has been focused on developing different PSS schemes to tackle the threat of damping oscillations to power system stability. This paper examines four different PSS models and investigates their performances on damping power system dynamics using both small-signal eigenvalue analysis and large-signal dynamic simulations. The four kinds of PSSs examined include the Conventional PSS (CPSS), Single Neuron based PSS (SNPSS), Adaptive PSS (APSS) and Multi-band PSS (MBPSS). A steep descent parameter optimization algorithm is employed to seek the optimal PSS design parameters. To evaluate the effects of these PSSs on improving power system dynamic behaviors, case studies are carried out on an 8-unit 24-bus power system through both small-signal eigenvalue analysis and large-signal time-domain simulations.     

Design of a nonlinear power system stabilizer using synergetic control theory

Electromechanical oscillations of small magnitude and low frequency exist in the interconnected power system and often persist for long periods of time. Power system stabilizers (PSSs) are traditionally used to provide damping torque for the synchronous generators to suppress the oscillations by generating supplementary control signals for the generator excitation system. Numerous techniques have previously been proposed to design PSSs but many of them are synthesized based on a linearized model. This paper presents a nonlinear power system stabilizer based on synergetic control theory. Synergetic synthesis of the PSS is based fully on a simplified nonlinear model of the power system. The dynamic characteristics of the proposed PSS are studied in a typical single-machine infinite-bus power system and compared with the cases with a conventional PSS and without a PSS. Simulation results show the proposed PSS is robust for such nonlinear dynamic system and achieves better performance than the conventional PSS in damping oscillations.     

Effective damping of local low frequency oscillations in power systems integrated with bulk PV generation

High penetration of renewable sources into conventional power systems results in reduction of system inertia and noticeable low-frequency oscillations (LFOs) in the rotor speed of synchronous generators. In this paper, we propose effective damping of LFOs by incorporating a supplementary damping controller with a photovoltaic (PV) generating station, where the parameters of this controller are coordinated optimally with those of a power system stabilizer (PSS). The proposed method is applied to damp local electromechanical modes by studying a system comprising a synchronous generator and a PV station connected to an infinite bus. The PV station is modeled following the instructions of the Western Electricity Coordinating Council. The problem is modeled as an optimization problem, where the damping ratio of the electromechanical modes is designed as the objective function. Constraints including upper and lower limits of decision parameters and damping ratio of other modes are considered by imposing penalties on the objective function. Different optimization algorithms are used to pursue the optimal design, such as political, improved gray wolves and equilibrium optimizers. The results validate the effectiveness of the proposed controller with PSS in damping local modes of oscillations.     

异步化汽轮发电机和PSS装置阻尼特性的比较研究

建立了加装PSS并考虑等效阻尼绕组作用的同步汽轮发电机单机无穷大系统线性化数学模型;同时建立了双通道励磁控制策略下异步化汽轮发电机在同步旋转X-Y轴系下的单机无穷大系统线性化数学模型。利用所建模型,对加装PSS后同步汽轮发电机的阻尼特性与采用双通道励磁控制策略的异步化汽轮发电机进行了分析和比较。通过比较,揭示了加装PSS后同步汽轮发电机阻尼特性得到改善的原因,分析了异步化汽轮发电机阻尼特性与励磁控制系数的关系,指出异步化汽轮发电机的同步转矩系数和阻尼转矩系数与发电机运行状态无关,明确异步化汽轮发电机在提高电力系统稳定性方面比PSS装置更具优势。     

Power system stabilizer design using Strength Pareto multi-objective optimization approach

Power system stabilizers (PSSs) are the most well-known and effective tools to damp power system oscillation caused by disturbances. To gain a good transient response, the design methodology of the PSS is quite important. The present paper, discusses a new method for PSS design using the multi-objective optimization approach named Strength Pareto approach. Maximizations of the damping factor and the damping ratio of power system modes are taken as the goals or two objective functions, when designing the PSS parameters. The program generates a set of optimal parameters called Pareto set corresponding to each Pareto front, which is a set of optimal results for the objective functions. This provides an excellent negotiation opportunity for the system manager, manufacturer of the PSS and customers to pick out the desired PSS from a set of optimally designed PSSs. The proposed approach is implemented and examined in the system comprising a single machine connected to an infinite bus via a transmission line. This is also done for two familiar multi-machine systems named two-area four-machine system of Kundur and ten-machine 39-bus New England system. Parameters of the Conventional Power System Stabilizer (CPSS) are optimally designed by the proposed approach. Finally, a comparison with famous GAs is given.     

采用协同控制理论的同步发电机非线性励磁控制

提出了一种基于协同控制理论的非线性励磁控制器。首先依据同步发电机励磁控制的基本要求和特点,选择机端电压、有功功率和转子角速度三个变量的偏差的线性组合构成流形,以保证有效控制机端电压和抑制系统功率振荡。然后以同步发电机非线性模型为对象,推导出了非线性协同励磁控制器（Synergetic excitation controller,SEC）的控制律,并根据电力系统的运行特性,探讨了控制器参数的选取原则。最后,单机无穷大系统仿真结果表明,无论在大扰动还是在小扰动下,所提非线性协同励磁控制器比常规的AVR+PSS方式下的励磁控制器都能更快更精确地调节机端电压,还能够有效地抑制系统的功率振荡。     

适应复杂电力系统多种运行方式的PSS优化配置

低频振荡的抑制是电力系统规划阶段和运行过程中必须考虑的一个重要问题。抑制低频振荡一般的方法是在励磁调节器上装设电力系统稳定器(PSS)。多机系统中，PSS的配置包括PSS安装位置的选择和参数整定。现有的研究工作主要考虑一种运行方式来进行PSS的优化配置，本文提出了一种同时适应系统的多种运行方式来进行PSS优化配置的方法。通过对西北电网三种典型运行方式的计算结果表明：为了获得更好的抑制低频振荡的效果，PSS的放大倍数不应限定为正值；如按一种运行方式对PSS的参数进行优化则对其它运行方式效果较差，而同时考虑多种运行方式，统一地进行PSS的优化配置则对各种运行方式都能良好地抑制低频振荡。     

Optimization and coordination of damping controls for improvingsystem dynamic performance

This paper presents a global tuning procedure for FACTS device stabilizers (FDS) and power system stabilizers (PSS) in a multi-machine power system using a parameter-constrained nonlinear optimization algorithm implemented in a simulation program. This algorithm deals with such an optimization problem by solving a sequential quadratic programming using the dual algorithm. The main objective of this procedure is to simultaneously optimize pre-selected parameters of the FDSs and PSSs having fixed parameters in coping with the complex nonlinear nature of the power system. By minimizing a nonexplicit target function in which the oscillatory rotor modes of the generators involved and suing characteristics between areas are included, interactions among the FACTS controls under transient conditions in a multimachine power system are improved. A multimachine power system equipped with a TCSC and an SVC as well as three PSSs is applied to demonstrate the efficiency and robustness of the tuning procedure presented. The results obtained from simulations validate the improvement in damping of overall power oscillations in the system in an optimal and globally coordinated manner. The simulations also show that the stabilizers tuned are robust in providing adequate damping for a range of conditions in the system     

Global tuning of power-system stabilizers in multi-machine systems

This paper presents a global tuning procedure for conventional PSSs in a multi-machine power system using a non-linear optimization algorithm implemented in a simulation program. The main objective of this procedure is to simultaneously optimize pre-selected parameters of those PSSs having fixed parameters in coping with the complex non-linear natures of the power system. By minimizing a non-explicit target function in which the oscillatory rotor modes of the generators involved and swing characteristics between areas are included, overall power oscillations at transient conditions in the multi-machine system are improved. A four-machine power system is applied to demonstrate the efficiency and robustness of the presented tuning procedure. The results obtained from simulations validate the improvement in damping of overall power oscillations in the system. The simulation also shows that the optimized PSSs are robust in providing adequate damping for a range of conditions on the system.     

Three basic constraints for the reasonable size of synchronous power systems

Power system interconnections bring primary economic and technical advantages. However, certain technical problems arise from the increasing size of the synchronous grid, such as centralized power dispatching and inter-area oscillations. From the technical viewpoint, this paper proposes three basic constraints to determine a reasonable size of synchronous grids, which are the synchronizing support effect disappearance constraint, the minimum oscillation frequency constraint of low frequency oscillations and the frequency stability constraint. First, the research results indicate that synchronous power systems would lose the essential power support advantage when synchronizing support effect disappears, which requires the synchronous system operated in direct synchronism, i.e. relative rotor angles all below 90 degree within the grid. Secondly, the total damping of generators with PSS tends to be negative when the frequency is lower than 0.3 Hz, and the lower frequency the worse damping effect. Thirdly, the frequency stability constraint depends on steady state frequency deviation requirement and transient state frequency deviation requirement. Based on general structures of power systems, the triangle criterion composed of the three constraints could provide useful references for regional or national synchronous power system interconnections and power system planning.     

发电机叠加型低励限制对电力系统动态稳定影响机制

当前发电机励磁调节器广泛配置有叠加型低励限制功能,该功能对电力系统动态稳定性有着重要影响,但其影响机制并未获得充分认识。文中基于扩展Heffron-Phillips模型,分析了模型新增回路系数随低励限制参数和机组工况的变化规律;采用电磁转矩分析法,将机组的阻尼转矩分解为低励限制提供的阻尼转矩、电力系统稳定器(PSS)提供的阻尼转矩、系统固有阻尼转矩和D系数阻尼转矩;推导分析了低励限制参数和工况变化对各部分阻尼转矩的影响机制。研究结果表明,通常较大的低励限制边界线斜率会导致低励限制提供的阻尼转矩分量变为负值,并且恶化PSS提供正向阻尼转矩的作用。通过典型系统的算例仿真进一步验证了所得结论的正确性。     

Optimal locations and tuning of robust power system stabilizer using genetic algorithms

Optimal locations and design of robust multimachine power system stabilizers (PSSs) using genetic algorithms (GA) is presented in this paper. The PSS parameters and locations are computed to assure maximum damping performance under different operating conditions. The efficacy of this technique in damping local and inter-area modes of oscillations in multimachine power systems is confirmed through nonlinear simulation results and eigenvalues analysis.     

同步电网合理规模的3个基本约束研究

电网互联可以充分发挥电网的经济效益,而同步电网规模充分扩大后将带来电网调度、低频振荡等问题。从纯技术的角度,提出决定同步电网合理规模的3个基本约束：频率稳定约束、低频振荡最低频率约束和同步功率支援效应消失约束。研究表明：稳态频率偏差指标比暂态频率偏差指标对同步电网规模的要求更高,因而同步电网频率稳定约束可根据稳态频率偏差指标计算;快速励磁控制在低频振荡频段内对发电机阻尼的贡献是负的,且振荡频率越低负阻尼越大,配备有电力系统稳定器的发电机总电气阻尼通常在振荡频率低于0.3 Hz后变负,且振荡频率越低负阻尼越大;同步功率系数是刻画同步功率支援效应的指标,若同步电网内2台机组间稳态功角差超过90°,同步功率支援效应将消失。从同步电网一般性结构出发进行研究,其研究结论对实际电网的互联方式与电网规模确定具有指导意义。     

Robust decentralized multi-machine power system stabilizer design using quantitative feedback theory

A new robust power system stabilizer (PSS) design using Quantitative Feedback Theory (QFT) for damping electromechanical modes of oscillations and enhancing power system stability is proposed in this paper. The design procedure is carried out on a multi-input–multi-output (MIMO), non-minimum phase and unstable plant. A multi-machine electric power system with system parametric uncertainties is considered as a case study. To show the effectiveness of the QFT technique, the proposed method is compared with a conventional PSS (CPSS) whose parameters are tuned using the classical lead-lag compensation and genetic algorithms. Several nonlinear time-domain simulation tests indicate that the suggested control scheme is robust to the changes in the system parameters and also to successfully reject the disturbances. The results also show that the performance of the QFT method given in this paper is more desirable than CPSS and genetic algorithm (GA).     

改善虚拟同步发电机阻尼特性的设计方法

虚拟同步发电机(virtual synchronous generators,VSG)控制基于虚拟同步机制可以增大电力系统等效转动惯量,改善电网稳定性.但是由于虚拟同步发电机模拟传统电机的机电暂态特性,传统电机的动态稳定性问题也因此被引入到虚拟同步发电机中.通过建立虚拟同步发电机的动态模型,发现线路电感会对系统等效产生...     

励磁系统动态增益对凸极发电机暂态稳定的影响

由于励磁系统动态增益对凸极发电机动态稳定性有显著影响,为改善电力系统阻尼,多需要调整该动态增益,进而配置电力系统稳定器。但在动态增益对发电机暂态稳定的影响方面,存在某些模糊认识,妨碍了相关工作的开展。文中首先分析了发电机暂态稳定与同步转矩的关系,将研究励磁控制系统动态增益对暂态稳定的影响转化为研究对同步转矩的影响,以便于数学推导。然后,对励磁控制系统动态增益影响凸极发电机同步转矩的机理进行了推导和算例计算,继之以单机系统、两机系统和实际系统仿真。计算和仿真结果表明,励磁系统动态增益在正常范围内变化时,对凸极发电机暂态稳定的影响很小,可以忽略。当为了改善电力系统阻尼而在正常范围内调整励磁控制系统动态增益时,不会对凸极发电机暂态稳定带来明显影响。     

基于阻尼转矩分析的电力系统低频振荡源定位

准确定位低频振荡参与机组并采取有效的控制措施以提高系统阻尼、快速平息系统振荡是大电网安全稳定运行的重要保障。为此,提出了一种基于总体最小二乘-旋转不变技术的信号参数估计(TLS-ESPRIT)和阻尼转矩分析(Damping Torque Analysis,DTA)方法进行低频振荡发生源定位的方法。该方法利用TLS-ESPRIT对发电机组的有功出力、角速度、功角信号进行模式分解,提取发电机高度参与的振荡模式,采用最小二乘拟合方法计算发电机高度参与振荡模式的阻尼转矩系数,然后根据阻尼转矩系数判定发电机是否为该振荡模式的振荡源。分别以4机2区和10机39节点系统为例进行仿真验证。仿真结果表明,所提出的振荡监测方法能够准确定位电力系统低频振荡源,且通过振荡源对其自身的控制能够有效地平息系统中的低频振荡现象。     

Damping controller design for power system oscillations usingglobal signals

This paper describes a new power system stabilizer (PSS) design for damping power system oscillations focusing on interarea modes. The input to the PSS consists of two signals. The first signal is mainly to damp the local mode in the area where PSS is located using the generator rotor speed as an input signal. The second is an additional global signal for damping interarea modes. Two global signals are suggested; the tie-line active power and speed difference signals. The choice of PSS location, input signals and tuning is based on modal analysis and frequency response information. These two signals can also be used to enhance damping of interarea modes using SVC located in the middle of the transmission circuit connecting the two oscillating groups. The effectiveness and robustness of the new design are tested on a 19-generator system having characteristics and structure similar to the Western North American grid     

Coordinated stabilizing control for large-scale interconnected power systems,by superconducting magnetic energy storage unit and power system stabilizers

The purpose of large-scale power system interconnection is to achieve extremely economical and reliable power generation and transmission. It has established the present power systems of high quality. On the other hand, in the large power systems with complex configuration, an undamped power swing with low frequency caused by the synchronous power between interconnected systems tends to occur as well as an undamped power swing caused by the synchronous power of specific generators. Several coordinated stabilizing control schemes for the power systems by sets of power system stabilizers (PSSs) have been investigated so far. PSS is very effective for the stabilization of power swing among a few specific generators because the function of PSS is achieved by the voltage control using the generator field winding circuit. However, it seems that PSSs do not have sufficient ability to stabilize the power swings between interconnected systems. In this paper, the superconducting magnetic energy storage (SMES) which is significantly effective for the power swings between interconnected systems is introduced and a coordinated power system stabilizing control by SMES and PSSs is proposed. The advantages of the proposed control scheme are: 1) high efficiency of the controller by the distribution of functions; 2) independency of the control design for PSS and SMES; and 3) robustness of the controller, and so on.     

Chaotic ant swarm optimization for fuzzy-based tuning of power system stabilizer

In this paper, chaotic ant swarm optimization (CASO) is utilized to tune the parameters of both single-input and dual-input power system stabilizers (PSSs). This algorithm explores the chaotic and self-organization behavior of ants in the foraging process. A novel concept, like craziness, is introduced in the CASO to achieve improved performance of the algorithm. While comparing CASO with either particle swarm optimization or genetic algorithm, it is revealed that CASO is more effective than the others in finding the optimal transient performance of a PSS and automatic voltage regulator equipped single-machine-infinite-bus system. Conventional PSS (CPSS) and the three dual-input IEEE PSSs (PSS2B, PSS3B, and PSS4B) are optimally tuned to obtain the optimal transient performances. It is revealed that the transient performance of dual-input PSS is better than single-input PSS. It is, further, explored that among dual-input PSSs, PSS3B offers superior transient performance. Takagi Sugeno fuzzy logic (SFL) based approach is adopted for on-line, off-nominal operating conditions. On real time measurements of system operating conditions, SFL adaptively and very fast yields on-line, off-nominal optimal stabilizer variables.